Fusing multiple sensors of same type using robot_localization.

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Hi, In order to perform SLAM or Localization, you need both Proprioceptive sensors (Internal state like an odometer, IMU, wheel encoder) and Exteroceptive sensors (external state like laser scanners). You need to use internal measurements to perform prediction with a given motion model. For correction step, you need to use external measurements like laser scans.

If you use wheel encoder system, you need a mathematical model to predict the next state of the robot in the prediction step of the EKF. you can use two velocity inputs or counts from wheel encoder as control inputs for state transition equations (prediction step). For example, two-wheel differential-drive-mobile robot. Then you can do correction using external measurements.